Wireless receiving system



Oct. 30,1934. I Y 1,978,534

- I L H. SCHOTANUS A STERINGA IDZERDA WIRELESS RECEIVING SYSTEM Filed Feb. 11, 1931 m HM MW JMW fl/w aiw a.

Patented Oct. 30, 1934 UNITED STATES 1,978,534 WIRELESS RECEIVING SYSTEM Hanzo Henricus Schotanus a Steringa Idzerda,

The Hague, Netherlands Application February 11, 1931, Serial No. 515,106 In the Netherlands February 15, 1930 8 Claims. I (Cl. 25020) The invention relates to wireless receiving systems in which a reduction of damping is effected in one or more of the high frequency circuits. In the known receiving systems of this kind the detector tube is generally back-coupled. A drawback of such a system is that due to the backcoupling it is very difficult to adjust the detector tube to obtain a maximum of demodulating efficiency. This difficulty is especially experienced when anode rectification is used. For, in this case the demodulating efficiency depends on the point of the anode current characteristic in which the tube is operating. Using grid rectification on the contrary it is the working point on the grid current characteristic which is of more importance. When anode rectification is used the modification of the dynamic steepness of the anode current characteristic brought about by controlling the grid of the demodulator tube causes the working point of this tube to be shifted outside the region in which the maximum rectification is obtained. Consequently anincrease of reaction leads to a decrease of demodulator efficiency and, accordingly to a detrimental ratio between the amplitude of high and low frequency currents in the output circuit of thedemodulator.

The invention removes this difliculty by using the detector tube for demodulating only, the reaction, which serves for effecting a reduction of damping in one or more of the high frequency circuits precedingthe demodulator, being caused by one of the low frequency tubes following the demodulator. By doing so, not only the rectifying action of the demodulator is improved but it will also be much easier to keep the receiving system on the threshold of self-oscillation and to obtain gentle setting in of oscillation. The reason is that the tube bringing about thereaction (that is, the low frequency tube) has its working point on a straight portion of a long characteristic where the steepness is as arule much greater than that in the working point of the characteristic of the reactively coupled detector tubes hitherto used. Further the straight characteristic of the tube producing reaction in a system according to the invention tends to make the generated oscillation more purely sinusoidal, which appears from the fact that oscillating reception becomes possible without causing distortion of the signals. As it is knownatmosphericsa're strongly reduced byoscillating reception, without decrease of signal strength. r

Thesystem according to the invention is preferably so constructed that some high frequency energy is transmitted through a small condenser from one of the high frequency circuits preceding the demodulator to the control electrode of one of the low frequency tubes following the demodulator. After amplification by the low frequency tube 60 the said high frequency energy is returned from the output side of this tube to one or several of the high frequency circuits. Thereby the small condenser serves for blocking the low, frequency voltages which might take rise on the control electrode of the low frequency tube due to the demodulation. In such a system it is of-great importance to take measures in order to prevent the coupling device between the low frequency tube bringing about the reaction, and the preceding tube, from being reached by high frequency currents either from the side of the control electrade of the low frequency tube or from the side of the demodulator. This tends to make the separation between demodulationand reaction more complete, thereby preventing certain low frequency parts of the system from being loaded with high frequency currents. The output side of the demodulator will preferably be short circuited for high frequency currents (by means of a condenser), so that no high frequency voltages can occur on the anode, which might decrease the rectifier efficiency.

The system according to the invention will be elucidated by means of the drawing showing three diiferentmodifications in which only those parts are shown which are necessary to understand the principles of the invention. In the figures denotes theusual source of anode current.

In Fig. 1 two tubes, 1 and- 2, are shown, the

first of which serves as a demodulator and the second as a low frequency amplifier. Preceding these tubes one or more high frequency tubes and following them one or more low frequency tubes may be provided if necessary.

r The input circuit of the demodulator 1 comprises a tuned oscillatory circuit 3, 4 of any form. Between the demodulator 1 and the low frequency tube 2a coupling element 5 is provided which may be of any known form (for instance a coupling transformer, a coupling resistance, a cou-- pling coil etc.). Following the low frequency tube 2 a similar coupling element6 may be provided for connecting the tube 2 to the next tube or toanother current consuming device (Such as a transmission line, a loud speaker etc.).

In order to separate the demodulation from the reaction a condenser 7 is provided transmitting a certain amount of high frequency energy from the oscillatory circuit 3, 4 to the control electrode of the low frequency tube 2. This energy is amplified by the tube 2 and transmitted e. g, over a condenser 9 to a reaction coillO coupled to the oscillatory circuit 3, 4. The output 7 the anode of the demodulator l and the coupling element 5. Norcan the high f requency oscillations occurring on'fthefcontrol' electrode of the tube 2 flow off through the coupling element 5, due to the presence of a choke 13 providedbetween the grid of tube 2 and the coupling element 5. As pointed out the condenser 7 serves for blocking the low frequency currents appearing on the control electrode of the tube 2 (due tov 'adjusted than in the arrangements hitherto known. I

It is obvious that the circuit for supplying a certain amount of high frequency energy tothe tube Z'rnay also be connected to another of the oscillatory circuits than to that preceding the detector 2. Neither is it necessary to use the first low frequency tube for bringing about the reaction. Further the manner in which the feed back to the high-frequency circuit or circuits is effected is arbitrary as well as the arrangement of the high and low frequency couplings between the tubes.

In Fig. 2 a modification of the invention is shown in which the high frequency energy for the control electrode of the low frequency tube bringing about the reaction is inductively derived from one of the oscillatory circuits. The arrangement is substantially the same as that of Fig. l, the only difference being that the condenser 7' for blocking the low frequency currents is connected to the cathode side of the osciilatory circuit 3, 4, and is in series with a coil'l'l coupled to the coil 3. In this case too the tube '1 may be preceded by one or more high frequency tubes.

The invention is'of great advantage when used in connection with a receiving system in which the oscillatory circuit or circuits in the high frequency portion of the system comprises a series connection of a small condenserand an L, Ccir- -cuit (flywheel circuit) nearly tuned to the received wavelength and forming together with the small condenser a series tuned resonance circuit.

Such a receiving system is shown e. g. in Fig. 3,

" it corresponds to the system of Fig. 1 with the exception, however, 'of a condenser 15 and a series tuned circuit 3, 4 being provided between the anode of the last high frequency tube 14 andth'enegative side of the cathode thereof. The'anode of the tube 14 is supplied with current over a choke or a resistance 16. If 'in'this case. as shown in the figure, the condenser 7 instead of being conneotedto the grid of the demodulator 1 is connected to theanode of the preceding tube 1a, the advantage is obtained that the shunt capacity 18 of the low frequency portion of the system will have less'in-fluen'ce on the grid of the demodulator 1-. Meanwhile even when the condenser '7 is connected to the control electrode of the tube 1 the fundamental'improvement will be obtained produced by separating the demodulation from the reaction.

LWh'at'I claim is:

1. In a wireless receiving system comprising a "'demodulating tube preceded by at least one high frequency oscillating circuit, and a low frequency tube having a control electrode and an output electrode, a connection avoiding the demodulator tube for supplying a restricted amount of high-frequency energy from one of said high frequency circuits to the control electrode of the low frequency tube, and a connection for returning the high frequency energy from the output electrode of the low frequency tube to one of the said high frequency oscillating circuits, said connections eifecting a reduction of the damping in the high frequency circuit.

2. A system according to claim 1 in which the connection for supplying high frequency energy from a high frequency circuit to the control electrode of the low frequency tube includes a condenser.

3. In a wireless receiving system comprising a demodulating tube having a grid and a high frequency oscillating circuit connected to said grid, and a low frequency tube having a grid and an anode, adirect connection avoiding the demodulating tube and including a condenser between said grids, and a connection including a condenser between said anode and said oscillating circuit.

- 4. In a wireless receiving system comprising a demodulating tube having a cathode and a high frequency oscillating circuit connected to said cathode, and a low frequency tube having a grid and an anode, a direct connection avoiding the demodulating tube between said cathode and said grid including a condenser and a coil inductively coupled. to the-oscillating circuit, and a connectionbetween said anode and said cathode including a condenser and a coil inductively coupled to the oscillating circuit.

5.-A system according to claim 1 in which at least that high frequency oscillating circuit from which the high frequency energy is supplied to the low frequency tube, comprises a series connection of a small condenser and a parallel tuned circuit including an inductance and a capacity, the connection for supplying high frequency energy to the low frequency tube being connected g to the end of said series connection and including a condenser.

6. A system according to claim 1 in which the demodulator tube has an output circuit and a coupling element is interposed between said tubes, and means are provided for preventing high frequency energy from reaching the coupling element from the output circuit of the demodulator.

v'7. A system according to claim 1 in which a couplingelement is interposed between said tubes and means are provided for preventing high frequency from reaching the coupling element from the control grid of the low frequency tube.

8. A system according to claim 1 in which the connection for returning high frequency energy from the output electrode of the low frequency tube to a high frequency circuit includes a condenser.

HANZO HENRICUS SCI-IOTANUS A STERINGA IDZERDA. 

